Many electronic devices include haptic elements to provide feedback to a user. For example, an electronic device such as a cellular telephone may leverage haptic elements to inform a user of an incoming call. In some examples, a haptic element may provide feedback through sustained or intermittent vibration over a period of time. Electronic devices which may benefit from haptic elements may include cellular telephones, smart phones, personal digital assistants, tablet computers, laptop computers, track pads, wearable devices, health devices, sports accessory devices, peripheral input devices, and so on.
Most haptic elements include an eccentric mass coupled to the rotating axis of an electric motor. When the motor rotates the eccentric mass about a shaft or other axis the haptic element typically experiences axially asymmetric forces, displacing the mass within a plane perpendicular to the axis of rotation. After reaching a sufficient angular velocity, the displacement of the mass may be perceived as a sustained vibration.
In other cases, a haptic element may be repeatedly activated and deactivated to simulate a pulsed vibration. Many haptic elements are structurally coupled to the housing of an electronic device, such that when the haptic element is activated, the electronic device housing vibrates.
In certain examples, the time required for the motor to reach the speed necessary for vibration to be perceptible (e.g., spin-up delay) may be distracting, confusing or frustrating to a user, even if the delay is minimal. In addition, a spin-up delay may undesirably limit the frequencies at which a haptic element may be pulsed. In still further examples, an eccentric mass haptic element may perceivably vibrate before reaching a maximum vibration intensity. In such a case, a user may perceive a haptic feedback of progressive intensity instead of a distinct and well-characterized haptic feedback.
Accordingly there may be a present need for an improved haptic element.